While Vettel has faith that long-term improvements by Renault can help lift his team back to the front of the field, he believes that tweaks tried out during Bahrain testing will help it make progress already.
"We made some improvements in the test," said the German. "We made some improvements with the car and also with our power unit, so all in all we should expect a step here. But how big the step is we need to wait and see.
"Surely it will be a massive surprise if we could close down the gap [to Mercedes] here.
"We have to be realistic and go with the results from the first couple of races, which is more or less [a gap of] one second per lap.
"To close that in one leap is hopefully not impossible, you can wish to do that, but we have to stay realistic."
With Mercedes having proven quick at Shanghai in the past, and being a dominant force right now, Vettel sees no reason to believe he can stop the German car manufacturer yet.
"I think Mercedes are probably favourites going in," he said. "For us we try to be as close as we can. What is realistic? If we can be in the top five that is good for us where we are right now.
"We are not where I want to be yet in terms of how I feel in the car, but there have been a lot of changes and a lot of new stuff to play with, and new stuff to adapt to.
"We are still learning as well with the car. That seems to be the biggest challenge right now."
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